1. Field of the Invention
The invention relates to a method and apparatus for obtaining a perceived color transient improvement, and to a television receiver incorporating such an apparatus.
2. Description of the Related Art
U.S. Pat. No. 5,012,331 discloses a video enhancement apparatus for a graphics encoder which extracts "sine-squared" (haversine) pulses representing absolute values for the derivatives of R-Y and B-Y color-difference "sine-squared" transitions; multiplies by offset, sign-inverted luminance, and adds the luminance-weighted "sine-squared" pulses to the composite video as color enhancement signals which exceed the NTSC-legal chroma bandwidth but are within the NTSC-legal luminance bandwidth. The pulses augment luminance during chroma transitions, restoring luminance contributions from chrominance which are lost when chroma subcarrier rise times and bandwidth are limited by NTSC broadcast requirements. This is desirable because NTSC-defined colors with a low luminance (Y) component derive relatively more of their visible brightness from chrominance components. Chrominance subcarrier rise time limiting therefore visibly darkens color transitions with low luminance more than color transitions involving relatively high luminance. The resulting augmentation of luminance during color transitions sharpens the apparent resolution on television receiver or monitor cathode ray tubes without extending chrominance bandwidth requirements necessary to prevent chrominance-luminance crosstalk.
European Patent Application EP-A-0,621,732, corresponding to U.S Pat. Nos. 5,663,769 and 5,621,480, discloses an image correction circuit having a variable gain amplifier for amplifying an extracted high-frequency component of a luminance signal in such a manner that the gain thereof is increased when detected color density is high, and is reduced when the detected color density is low, and a slice circuit for slicing the outputted amplitude of the variable gain amplifier at a prescribed value, wherein a corrected luminance signal is obtained by combining an image quality correction signal outputted from the slice circuit with the luminance signal to be corrected.